Portable electronic devices such as notebook computers rely upon an external power source, such as an AC/DC adapter connected to a wall power outlet to charge an associated battery pack and power the operation of the connected electronic device. When the AC/DC adapter is removed from the electronic device, the battery pack takes over responsibility for powering the device and sustaining system operations. There are several existing power delivery and battery charging schemes utilized with electronic devices such as a notebook computer.
One power delivery and battery charging architecture uses a separate battery charging and system power bus scheme. This is the dominant power delivery and battery charging scheme used in notebook computers today. The configuration provides two power flows from the adapter input. One path forms the power system bus which provides the power to all components within the notebook computer except for the battery. The second path comprises the battery charging path. As the battery is being charged, it is isolated from the system power bus. Once the adapter is unplugged, the battery is connected to the system power bus. With such a power delivery architecture, when an adapter is present, the voltage on the system power bus equals the adapter voltage, typically 19 volts. When the adapter is unplugged, the voltage on the system power bus equals the battery voltage, typically 16.8 to 11.2 volts for a four cell series battery pack or 12.6 volts to 8.4 volts for a three cell series battery pack. Thus, the combined voltage range using the adapter mode and the battery power mode varies from the adapter voltage down to the battery voltage. Due to the wide variation of the input voltage values, the downstream converter design must consider the voltage stresses at a high voltage mode, the adapter mode, and thus make compromises in the component selection, thermal management considerations and other electrical performances of the architecture.
A second power delivery configuration comprises the combined battery charger and system power bus architecture. This configuration was proposed to overcome the shortcomings associated with the wide input voltage range of the separate battery charging and system bus architecture. Within this configuration, the adapter input voltage is stepped down to a lower voltage level by a buck converter regulator. While charging the battery, the same output voltage of the buck regulator is connected to the system bus to provide the same voltage for the other devices within the notebook computer as is provided by the battery. Once the battery is fully charged, it is isolated from the system power bus while the adapter is connected. Once the adapter is unplugged, the battery is reconnected to the system bus to sustain continuous system operations. With the help of the buck converter, the system power bus has a narrower voltage range typically determined by the voltage range of the battery within the device. This power delivery architecture is often referred to as narrow VDC or NVDC1. With the application of the narrower voltage range on the system bus, the downstream converters can be designed with better component selection, higher operational efficiency and better system performance. However, the buck converter is serving as a pre-regulator of the adapter input voltage to the system. The overall power delivery efficiency is a multiple of the efficiency of the pre-regulator, and the efficiency of the downstream voltage range. The overall system efficiency may actually be lowered depending upon the design. Since the buck converter regulator delivers the total power to the system, the thermal stresses may be higher with a lower efficiency compared to the architecture of the separate battery charging and system power bus scheme described previously.
An adapter battery charger architecture has also been used. In this configuration, the adapter directly serves as the battery charger and the system power bus is also derived from the same adapter input. A power monitoring circuit provides feedback on the status of the battery and the power system to the adapter in order to regulate the voltage from the adapter. The adapter battery charger configuration is referred to as NVDC2. Similar to the NVDC1 configuration, NVDC2 has a narrow input voltage range and enables better design of the downstream power converters. NVDC2 facilitates the design of a connected notebook computer, but raises additional issues on the adapter design and the interface between the adapter and the connected electronic device such as a notebook computer. This configuration significantly increases the output current requirement of the adapter and thus makes the adapter less efficient. The adapter also has more power to dissipate which aggravates the thermal issues within the adapter. The configuration also increases the adapter to notebook cabling requirements and raises new issues related to the adapter and notebook connectors. Thus, it would be desirable to have an adapter/battery charging configuration that would overcome the problems associated with the previously utilized architectures.